Metal nanoparticle-polymer composites comprising metal nanoparticles dispersed in a polymer matrix are new functional materials which are produced by combining metal nanoparticles with a polymer, which have different physical and chemical properties. Since these metal nanoparticle-polymer composites combine the advantages of the metal nanoparticles and the polymer and can be applied to a wide range of fields, they have received a lot of attention. For example, gold nanoparticles themselves have been applied in various fields, such as surface plasmon resonances, catalysts, nanomedicines, and bio-sensing. Gold nanoparticle-polymer composites comprising gold nanoparticles either adsorbed on the surface of a polymer or contained in a polymer matrix have been reported to have increased activity compared to gold nanoparticles themselves. In addition, with the rapid development of electric, electronic and energy technologies, the need for new materials having excellent functions has been emerged, and studies on metal nanoparticle-polymer composites have also been accelerated.
Conventional methods for producing metal nanoparticle-polymer composites may broadly be classified into an ex-situ method and an in-situ method.
The ex-situ method is a method of producing a composite by mixing previously prepared metal nanoparticles with a polymer as disclosed in Korean Patent No. 10-1519749. In this case, the polymer matrix simply acts as a dispersing agent. This ex-situ method has problems in that an additional process for preparing nanoparticles is required and the agglomeration and precipitation of metal nanoparticles occur during mixing of these metal nanoparticles with the polymer which is a highly viscous liquid. Furthermore, once the nanoparticles are agglomerated, the agglomerated nanoparticles are not easy to disperse uniformly even when an external force is applied thereto.
Meanwhile, the in-situ method is a method of forming metal nanoparticles by reducing a metal nanoparticle precursor on a polymer (or polymer solution) matrix by a physical or chemical method. This class includes: Korean Patent No. 10-1295671 which discloses reducing an organic metal compound, mixed with a polymer matrix, into metal nanoparticles by heat treatment; Japanese Patent No. 0415884 which discloses producing metal nanoparticles by hydrolyzing a metal alkoxide adsorbed on the surface of a polymer; and Korean Patent No. 10-0811001 which discloses depositing a gaseous metal component on the surface of a polymer by plasma discharge in vacuum. The metal nanoparticle-polymer composite produced by the in-situ method has an advantage in that the metal nanoparticles are uniformly dispersed without being agglomerated. However, high-temperature heat treatment is required in the process of reducing a metal nanoparticle precursor, or a system for performing plasma deposition in a high vacuum state is required. When reduction is performed by a physical method, problems arise in that the layer thickness is not uniform and adsorption ability is low. Alternatively, when a metal nanoparticle precursor is reduced by a chemical method, the reduction is performed through a complex chemical reaction process, and hence the production yield is not high and the production cost is inevitably high. In addition, problems arise in that a process for post-treatment of a reagent used as a reducing agent is additionally required and the remaining reagent causes a pollution problem.
It is well known that when metal nanoparticles are applied to fields, such as biosensors or nanomedicines, it is important to control the shape of the metal nanoparticles. However, according to reports that gold nanoparticle-polymer composites were produced by the in-situ method, gold nanoparticles have a spherical shape or an irregular shape, and the shape is not easily controlled. In order to control the shape of the gold nanoparticles included in the composite, various factors, including temperature, a reducing agent, an additive for shape control, and the like, should be changed. For this reason, problems arise in that a process consisting of several steps is required for synthesis and in that an unexpected intermediate is produced which should be removed.
Above all, both the ex-situ and in-situ methods have a problem that polymer production requiring a complicated organic synthesis process must be preceded. Therefore, it is needed to develop a method that can easily control the shape of metal nanoparticles and can produce in a simple manner a metal nanoparticle-polymer composite in which metal nanoparticles are uniformly dispersed without being agglomerated.
The present inventors previously found that a polymer thin film can be produced by applying plasma to the interface between liquid monomers. Based on this finding, the present inventors filed a patent application (Korean Patent Application No. 10-2014-0148118). Through a subsequent study on this finding, the present inventors have found that a metal nanoparticle-polymer composite can be produced in a simple manner by applying the above-described method for producing the polymer thin film, thereby completing the present invention.